ares: remove fd from multi fd set when ares is about to close the fd

When using c-ares for asyn dns, the dns socket fd was silently closed
by c-ares without curl being aware. curl would then 'realize' the fd
has been removed at next call of Curl_resolver_getsock, and only then
notify the CURLMOPT_SOCKETFUNCTION to remove fd from its poll set with
CURL_POLL_REMOVE. At this point the fd is already closed.

By using ares socket state callback (ARES_OPT_SOCK_STATE_CB), this
patch allows curl to be notified that the fd is not longer needed
for neither for write nor read. At this point by calling
Curl_multi_closed we are able to notify multi with CURL_POLL_REMOVE
before the fd is actually closed by ares.

In asyn-ares.c Curl_resolver_duphandle we can't use ares_dup anymore
since it does not allow passing a different sock_state_cb_data

Closes #3238

1 files changed, 2 insertions, 1 deletions

diff --git a/lib/easy.c b/lib/easy.c
index 4de4e6522..d940b5d3e 100644
--- a/lib/easy.c
+++ b/lib/easy.c
@@ -966,7 +966,8 @@ struct Curl_easy *curl_easy_duphandle(struct Curl_easy *data)
   }
 
   /* Clone the resolver handle, if present, for the new handle */
-  if(Curl_resolver_duphandle(&outcurl->state.resolver,
+  if(Curl_resolver_duphandle(outcurl,
+                             &outcurl->state.resolver,
                              data->state.resolver))
     goto fail;